Recent years have seen a marked increase in interest in fuel cells for the generation of electric power. One area where interest is high is in the design of propulsion systems for vehicles. As is well known, a typical fuel cell combines hydrogen and oxygen to generate electricity which may then be used to power an electric motor which can be used to provide propulsion for a vehicle.
More recently, there have been a variety of proposals of fuel cell systems employing a so-called reformer. Reformers are chemical processors which take an incoming stream of a hydrocarbon containing or hydrocarbon based material and react it with water to provide an effluent that is rich in hydrogen gas. This gas, after being further treated to rid it of fuel cell poisoning constituents, most notably carbon monoxide, is then provided to the anode side of a fuel cell. Ambient air is provided to the cathode side of the fuel cell. The oxygen in the air and the hydrogen in the anode gas are reacted to provide water and generate electricity that may be used to power a load such as an electric motor.
The reformer must receive the fuel and water in vapor form. Consequently, if the disadvantage of high pressure vessels associated with some pure hydrogen fuel cells is to be avoided, some means of carrying the fuel in a liquid form in a tank comparable to gasoline or diesel fuel tanks must be provided along with a means for vaporizing the water and the fuel prior to its admission to the reformer. While for many non-vehicular applications, the matter of vaporizing the water and the fuel may be handled relatively simply, the problem is much more difficult where the production of electricity by the fuel cell is expected to respond rapidly to a change in electrical load. In the vehicular context, this means that the fuel cell must respond rapidly to changes commanded by the driver of the vehicle through changes in the position of the fuel cell equivalent of a conventional gas pedal.
It has been determined that the rapidity of response of the fuel cell to a commanded change depends on the mass of water and fuel in the vaporizer that feeds vaporized water and fuel to the reformer. The greater the mass of fuel and water in the vaporizer, the longer the response time. Consequently, it has been determined that to be effective in fuel cell systems powering loads which require rapid response to a change in conditions, the mass of fuel and water in the vaporizer be held to an absolute minimum. To meet this requirement, it is highly desirable that the fuel and water side of the vaporizer have as small a volume as possible.
In vehicular applications, it is also highly desirable that the overall vaporizer be as small in size as possible in terms of volume and in weight. Bulk and weight are highly disadvantageous in that weight reduces the overall fuel efficiency of the vehicle and bulk reduces the load carrying capacity of the vehicle to the point that it is impractical to provide a vehicle that can compete with conventionally powered vehicles in use today. It is also desirable to achieve a very short system start-up time.
The present invention is directed to overcoming one or more of the above problems.